Ever since the term “flying saucer” was first introduced in 1947, the concept of a circular flying craft has become a staple of popular culture. Unlike conventional aircraft in which lift is produced by the difference between the air flowing over the top versus the bottom of a wing, most flying saucers have proposed using the aerodynamic effect of a spinning disc to at least partially generate the lift required for the craft. The flying disc toy known as the Frisbee® is perhaps the best example of this principle. While numerous concepts relating to spinning, flying disc-shaped craft have been put forth in a variety of patents and publications, a practical embodiment of a self-powered flying saucer has yet to be developed.
The concept of a heavier-than-air craft supported by a fluid instead of wings or rotors predates even the Wright brothers' first flight. U.S. Pat. No. 730,097 issued in June 1903 described an airplane controlled by a jet propulsion arrangement that proposed using a pendulum valve to control the operation of the jets as an automatic means to keep the craft in equilibrium. Despite numerous attempts to realize the concept of a craft suspended by downward directed jets, it was more than sixty years later before the Harrier jump jet actually achieved this goal with the first practical vertical-take-off-and-landing (VTOL) aircraft. Even so, the difficulty in controlling and maneuvering such a VTOL aircraft on both take-offs and landings, as well as transitions from vertical to horizontal flight, continues to plague the general acceptance of VTOL aircraft as evidenced by the ongoing difficulties with the US Marine Corps' V-22 Osprey aircraft.
Various attempts have been made to use the inherent stability of a spinning disc or multiple spinning disc arrangement in order to stabilize a fluid suspended flying craft Examples of the use of jet propulsion in connection with a spinning disc are shown in U.S. Pat. Nos. 3,199,809, 3,503,573, 3,946,970, 4,566,699, 5,351,911, 6,050,250, 6,302,229, 6,371,406, 6,375,117, 6,572,053, and 6,575,401. Other examples of spinning annular rings or discs in a saucer-shaped craft are shown in U.S. Pat. Nos. 2,863,261, 4,214,720, 4,273,302, 4,386,748, 4,778,128, 5,072,892, 5,259,571, 6,053,451, 6,270,036, and 6,398,159.
Another approach to supporting a heavier-than-air craft has involved the use of ducted fans, instead of jets or rotors, to provide the necessary thrust for supporting and propelling the craft. Patents directed to the use of ducted fans to support a heavier-than-air craft date back to as early as 1872 and include craft that relied solely on ducted fans (e.g., U.S. Pat. Nos. 129,402, 905,547, 931,966, 996,627, and 1,816,707), as well as craft that used ducted fans in combination with wings (e.g., U.S. Pat. Nos. 1,291,345, 1,405,035, 1,959,270, 2,461,435, 2,968,453 and 6,547,180) or craft using ducted fans in a helicopter-like craft (e.g. U.S. Pat. Nos. 1,911,041, 2,728,537, 3,199,809, 5,503,351, 6,402,488, and 6,450,446).
The first non-spinning disc shaped aerial craft with a single central ducted fan arrangement, as described in U.S. Pat. No. 2,567,392, used shutters to control airflow and orientation of the craft. The problem with this arrangement is similar to the problems encountered with helicopters, namely the rotation of a single fan imparts a one-way spin or torque that must somehow be counteracted in order for the craft to remain stable. Most central ducted fan arrangements have since utilized the concept of two counter-rotating blades spinning on the same axis in opposite directions to overcome this single-fan torque problem. The most famous application of this concept was the 1950's Hiller flying platform as described in U.S. Pat. No. 2,953,321 that was based on work dating back to 1947 by Zimmerman. The Hiller flying platform was controlled by having the operator shift his weight to alter the center of gravity of the craft.
Other craft that use the co-axial counter-rotating blades for a central ducted fan arrangement have used vanes, louvers and duct arrangements to control airflow from the ducted fans in order to control orientation of the craft (e.g., U.S. Pat. Nos. 2,728,537, 3,442,469, 3,677,503, 4,795,111, 4,804,156, 5,178,344, 5,203,521, 5,295,643, 5,407,150, 6,450,445, and 6,588,701). Patents also have described craft that use a pivoting central ducted fan arrangement to control airflow and orientation (e.g., U.S. Pat. Nos. 2,730,311, 2,876,965, 2,968,318, 5,421,538 and 6,224,452). Still other patents have described central ducted fan craft that used variable pitch angle blades to control the airflow and orientation of the craft (e.g., U.S. Pat. Nos. 2,968,318, 3,002,709, and 3,395,876). The addition of tail fins and tail rotors or tail jet engines to a central ducted fan craft has been described in several patents (e.g., U.S. Pat. Nos. 2,988,301, 4,796,836, 5,035,377, 5,150,857, 5,152,478, 5,277,380, 5,575,438, 5,873,545, 6,270,038, 6,457,670, and 6,581,872). The addition of a gyroscope mounted to and rotated by the propellers of the ducted fan to aid in stabilization of the craft has been described in U.S. Pat. Nos. 4,461,436 and 6,604,706. Combinations of one or more of the control techniques have also been proposed in many of these patents as well as in U.S. Pat. No. 4,196,877.
Ever since the 1950's, there have been sporadic research projects sponsored primarily by various military organizations on the design of enclosed rotorcraft vehicles. All of these designs to date have utilized a single-axis rotor inside a cowl or protective ring arrangement that forms a ducted fan. The most successful implementation of a single-axis counter-rotating ducted fan arrangement has been the Cypher™ unmanned air vehicle (UAV) from United Technologies Corp. that operates as a single-axis VTOL craft. The Cypher™ has been effectively used as a drone surveillance probe by the military when remotely piloted by experienced UAV pilots.
Recently, the military has started funding development of smaller unmanned air vehicles known as Organic Air Vehicles (OAVs) that are intended to be small (<24″ diameter) field-deployable remote controlled flying vehicles. Two multi-million dollar research and development contracts were granted in 2001 for the OAV program. Both contracts sought to extend the single-axis VTOL concept that is the basis for all military enclosed rotorcraft into a number of smaller sizes. The VTOL craft for the OAV program is designed to be oriented upright for takeoff and landings and transition into a sideways orientation for flight. As one might expect, the trickiest part of controlling this craft occurs during the transitions between vertical and horizontal orientations.
In March 2002, the OAV design from Honeywell known as the Kestrel was selected for further funding. The Kestrel design is a conventional VTOL single axis rotorcraft that looks like a 5 pound coffee can with bunny ears and legs and is powered by a gas engine in the center and a pair of fuel carrying/payload bearing pods mounted on the sides. The Kestrel design has three sizes from 9-29 inches, with payloads ranging from 8 ounces to 18 pounds and an expected price tag of $10,000-$25,000 per unit. Available information indicates that these OAV's are being designed for automated self-piloting based on GPS coordinates and complex object recognition vision systems. Currently available information indicates that the smaller OAV models of the Kestrel project are still not ready for use. For more information on the current status of unmanned aircraft development, see “Future of Unmanned Aviation,” Popular Science, June, 2003.
One alternative to the VTOL central ducted fan arrangement is the use of a pair of counter-rotating ducted fan arrangements that has been proposed in both side-to-side and front-and-back positions in a craft (e.g., U.S. Pat. Nos. 2,077,471, 2,988,301, 3,752,417, 5,049,031, 5,064,143, 5,213,284, 5,746,930, 5,890,441, and 6,464,166). A very early proposal for a ducted fan craft using more than a pair of ducts was described in 1911 by Gridley in U.S. Pat. No. 1,012,631. Grindley showed the use of four ducted fans to produce a balanced (even) effect on the plane of the body of the craft, but no control arrangement for the fans was described. U.S. Pat. No. 4,795,111 described an alternate embodiment of a UAV that employed four ducts and briefly proposed altering fan pitch control or throttle control as a means for controlling this embodiment. U.S. Pat. Nos. 6,179,247 and 6,254,032 describe proposed flying passenger craft that use ten or more ducted fans arranged in an equidistant manner in a ring around the craft. Both patents briefly describe a control system that varies the throttle control of different engines. U.S. Pat. No. 6,179,247 also proposes the use of a moveable paddle system to deflect air for purpose of control, whereas U.S. Pat. No. 6,254,032 also proposes that each ducted fan is individually pivotable to control airflow direction.
Until recently, most development efforts in heavier-than-air craft that are fluid sustained using ducted fans of the like have been focused on larger passenger aircraft of UAVs. Recent advances in battery technology have generated a renewed interest in the field of remote controlled aircraft and smaller OAVs. Instead of conventional gas-powered engines, a combination of high-powered batteries and light-weight electrical motors have been used as replacement engines for model airplanes and model helicopters. While this represents an improvement in terms of simplicity and operability, model airplanes, and particularly model helicopters, are still expensive, complicated, temperamental and fragile hobby toys that can require months to build, learn, rebuild and master.
Various powered spinning disc toys and models have attempted to address the control and stability problems associated with model airplanes and model helicopters using many of the same approaches described above. These include single rotor model craft (e.g., U.S. Pat. Nos. 3,394,906, 3,477,168, 3,528,284, 3,568,358, 3,608,033, 4,065,873 and 5,429,542), dual counter-rotating rotor model craft (e.g., U.S. Pat. Nos. 2,949,693, 5,071,383, 5,634,839, 5,672,086, and 6,053,451) and even rocket or jet-powered models (e.g., U.S. Pat. Nos. 3,508,360 and 4,955,962). U.S. Pat. No. 5,297,759 describes a disc-shaped model craft that uses two conventional aircraft propellers mounted at an angle of about 30 degrees on the surface of the disc to rotate the disc to provide both lift and propulsion.
More recently, variations on the conventional model helicopter have been introduced utilizing multiple main rotors, each powered by a separate electrical motor. The Hoverfly® II is perhaps the best example of such a craft that utilizes three main rotors and a tail rotor in a classic helicopter format. The Ultimate Flying Saucer™, the GyroSaucer™ and the DraganFlyer III™ utilize four rotors (two pairs of counter-rotating rotors) in a helicopter-like fashion to provide lift for the model craft, but do not have a separate tail rotor. Instead, the DraganFlyer III™ uses three piezoelectric oscillation gyros to transmit flight data to an on-board computer to provide balanced reciprocal thrust among the rotors. Another variation on this approach is the Vectron™ Blackhawk that integrates a rotating outer ring with three rotor blades to provide lift for the craft.
Unfortunately, each of these craft is still difficult to control and maneuver and all of these craft rely on multiple conventional helicopter rotors to provide aerodynamic lift, rotors that are easily damaged in the event of a crash. Like all exposed rotor craft, these multi-rotor models are also inherently dangerous due to the exposed spinning rotors.
The most extensive research project using ducted fans instead of rotor blades was conducted by a research group at Stanford University for a NASA project to design miniature flying craft to be used for aerial mapping of Mars. The design known as a “mesocopter” calls for a very tiny battery-powered four rotor craft less than two inches across. In one version, the four tiny rotors are each shrouded in a protective ring. While the research is interesting, the project has no practical guidance on how to make a model-sized RC flying craft for here on Earth because of the differences in gravity and air density as compared to Mars.
A design concept for a model flying hovercraft powered by ducted fans has been proposed by a student at MIT. Although his design proposed the use of counter-rotating ducted fans to power the craft, he has never been able to make the design work. Control of his 4 ducted fan design was to be achieved by using three separately controlled fins, one for yaw, one for left-right and one for back-forth. While some interesting concepts were proposed, a workable prototype was never achieved and no further work on the project has been reported.
Whether the craft is a single-axis VTOL, ducted fan UAV or OAV, a multi-rotor model RC craft, or a multiple ducted fan craft, the main challenges with all of the existing designs for fluid sustained aircraft are case of control and stability of flight. Manually flying any of these craft requires extensive training and skills. Unfortunately, the automated self-piloting systems capable of attempting to assist with flying any of these craft are all based on the complicated and expensive inertial guidance auto-pilot systems used in airplanes today.
Existing autopilot systems, such as the state-of-the-art Honeywell Fault-Tolerant Air Data Inertial Reference System (FT/ADIRS), use one or more gyroscopes to sense rotation about an axis in the form of angular velocity detection. The FT/ADIRS, for example, is comprised of a six-sided structure holding six ring laser gyros and six accelerometers. A myriad of backup and redundant power supplies and computer systems are integrated with this system to prevent a mid-flight failure.
The basic reason for the use of very high precision laser ring gyros and multiple redundancies is that existing inertial guidance systems all rely on an initial static determination of the gravitational reference to be used by the system. In the case of an autopilot system, the gravitational reference or ground horizon reference is established when the plane is on the ground. This process, commonly referred to as boresighting, establishes the gravitational reference for down. Once this gravitational reference is established, it is essentially static and unchanging and the auto-pilot system uses the gyros to keep very precise track on a dead-reckoning basis of all changes in the attitude of the craft from the point of the ground plane reference. This complicated referencing to a static ground plane reference can be augmented dynamically by obtaining positional information from a global positioning satellite (GPS) system, but GPS systems are not precise enough to detect small changes in attitude of a craft on a continual basis.
Ideally, the ground plane reference could be dynamically updated on a continual basis when the craft was in the air, thus eliminating the need for the complicated gyro based inertial guidance systems. Unfortunately, mechanical sensors such as pendulums, gyros and piezo-accelerometers do not function the same in dynamic situations where the sensors are continually subjected to multiple acceleration fields. The impact of precession on those sensors means that the sensor readings will provide an incorrect ground plane reference. By example, a pendulum is a very simple and effective gravitational sensor in a static context. If a pendulum is subjected to a centripetal acceleration in addition to gravitational acceleration by swinging the pendulum in a circle, for example, then the “reading” of the pendulum will not point down. Instead, the pendulum will point in a direction that is a combination of both the gravitational acceleration and the centripetal acceleration. This phenomenon is further complicated in situations where the craft is in a parabolic dive, for example, when the tilt of the craft is equal to the rate of acceleration of the dive. In this situation, referred to as the “death spiral,” the forces on sensor are balanced so that the sensors typically give no useful output readings in this situation.
U.S. Pat. No. 5,854,843 describes a virtual navigator inertial angular measurement system that uses gyros to sense angular velocity and piezo-accelerometers to correct for drift in the gyros. While the piezo-accelerometers are referred to in this patent as “absolute” references, it is understood that these piezo-accelerometers are absolute only with respect to the initial gravitational ground plane established by a boresighting process. The need for this initial boresighting is confirmed by the fact that the invention touts the advantage of being stable for long periods of time. If an inertial guidance system were able to dynamically update its initial gravitational ground plane, then the need for “stability” over extended periods of time is eliminated.
Examples of current state of the art inertial navigational reference systems for aviation that use a gyro-based angular rate sensing arrangement similar to that described in U.S. Pat. No. 5,854,843 are shown in U.S. Pat. Nos. 5,440,817, 5,676,334, 5,988,562, 6,227,482, 6,332,103, 6,421,622, 6,431,494, and 6,539,290. While certain references indicate that a gyro sensor can be a gravitational detector of down, it must be understood that this statement is valid only under static conditions or in a limited set of acceleration circumstances where the output of the sensor is not compromised by the acceleration fields. U.S. Pat. No. 6,273,370 attempts to overcome these limitations by trying to keep track of different states of the sensor system and determining a course of action based on the different state conditions. Still, if the sensor system loses track of the state of the sensor system, even this arrangement cannot dynamically determine an inertial gravitational reference to use as a reference.
What is needed is a heavier-than-air flying craft that has the ability to hover and to perform vertical air movements like a conventional model helicopter, yet is easier to operate and more durable than existing flying machines.